cardiac & non-cardiac muscle enzymes- diagnostics

diagnostics 1

cardiac laboratory tests are used to

confirm our clinical suspicion of heart disease rather than to establish the diagnosis

cardiac enzymes measure the level of

enzymes that are linked with injury of heart muscles

cardiac enzymes

cardiac troponin

creatinine kinase

lactic dehydrogenase

myoglobin

CK

creatinine kinase

CK with different subtypes

CK isoenzyme CK-MB specific to the heart

LDH

lactate dehydrogenase

cardiac troponins

troponin I

troponin T

both troponin I and T are found in

heart muscles and are released into the blood stream when cardiac cells are damaged

troponin I

TnI

TnI

found only in the heart muscle, more sensitive for diagnosing acute MI

binds to actin in think myofilaments

troponin T

TnT

TnT

found in heart muscle and small amounts in other muscles

binds to tropomyosin

poor renal clearance (pt w/ CKD/ESRD or AKI) can cause decreased

clearance of troponin

in CKD pts, what should you be aware of in relation to troponin?

troponin levels lack specificity in pts with CKD

troponin elevations are mostly related to

ischemic myocyte injury due to acute coronary syndrome (Type I MI)

what is the first line test for evaluation pts with suspected acute MI? why?

cardiac troponin

bc troponin has the highest sensitivity and specificity for myocardial injury

We use high sensitivity troponin I in hospital to detect

troponin at much lower concentrations than what the conventional troponin tests can detect

• allows for more rapid diagnosis in pts in the hospital suspected to have acute MI

Troponin T and I are more sensitive and specific for. . .

myocardial injury than CK-MB

troponin is detectable in serum

3-6 hours after an acute MI begins

troponin reaches 95-99% sensitivity and specificity by

10 hours

troponin peaks at

24-48 hours→ peak level correlates with size of infarct

troponin remains detectable in serum for

10-14 days after the acute events (4x longer than CK levels) → allows for dx of an acute MI even more than a week after onset

cardiac troponins can detect. . .

lesser degrees of myocardial necrosis and is useful to diagnosis microinfarcts in CK-MB negative pts with ACS

troponin is used to r/o . . .

false positive CK-MB suspected acute MI

dx of acute MI

needs to be a rise and/or fall in cardiac troponin levels along with a clinical picture consistent with ACS

causes of troponin leak

cardiac biomarkers

troponins can be elated in conditions that

result in supply-demand ischemic mismatch (type II MI)

things that can cause troponin leaks

anemia, tachyarrhythmias, hypotension, hypertension, myocarditis, PE d/t RV ischemia, acute CHF, renal failure (CKD/AKI/ESRD), catheter ablation procedure, electrical cardioversions/defibrillators, CPR, PCI and CABG, post surgery, vigorous exercise, sepsis, critical illness

elevated serum troponin levels in pts with ACS may reflect

watershed injury or minor degrees of myocardial necrosis that result from microembolic from an unstable coronary atherosclerotic plaque

troponin levels may not rise until . . . . . after the onset of symptoms

6 hours

SO measurements need to be repeated if initial troponin levels are negative at < 6 hrs from onset of chest pain

serial troponins are crucial in the . . .

diagnosis (rise and/or fall)

CK is found in

the tissues of the heart, skeletal muscle, CNS, lungs

CK subtypes

CK-BB

CK-MB

CK-MM

CK-BB

brain tissue and smooth muscle

CK-MB

mostly in the heart muscle, but small amounts in skeletal muscles

CK-MM

skeletal muscle

CK rises for . . . . after the acute event and peaks at . . . .

several hours and peaks at 24 hrs

CK returns to baseline within

48-72 hrs

CK can be elevated from

non-cardiac sources; less specific to the heart

• skeletal muscle injury

  • trauma

  • surgery

  • IM injections

• myopathy or myositis

  • secondary to statins

  • rhabdomyolysis

• hypothyroidism

• renal disease (less affected by renal function compared to troponins)

CK-MB is the . . .

most specific CK isoenzyme to the heart

CK-MB is less sensitive and specific for

myocardial injury than troponin I or T

CK-MB is only marginally specific for . . .

acute MI and not a reliable lab value by itself to r/o acute MI

1/3rd of ACS pts have

elevated troponin levels but negative CK-MB

CK-MB is useful for clarifying the etiology of

myocardial injury in addition to troponin levels when diagnosis is not clear

CK-MB is used at times when the provider. . .

cannot discern chest pain etiology and do not have a reason for troponin elevation

CK-MB can be useful for diagnosing

reinfarction given it returns to baseline faster than troponin levels (which can persist for days)

LDH is found in

almost all body tissues but highest concentrations in the muscle, liver, kidneys, and RBCs

how many isoenzymes of LDH?

5 separate isoenzymes

LDH can be found in the heart, but . . .

elevation is very non-specific for cardiac cause

• not used in cardiology often

LDH-1

for myocardial injury

LDH serum levels rise more gradually 24-48 hrs after acute MI and peak at 3-5 days after the acute event

returns to baseline around 5-10 days

LHD-5

in liver injury

LDH-2 and LDH-3

in lung injuries and disease

if all LDH levels are elevated

suggests multi-system organ disease

LDH is falsely positive if

hemolysis occurs, strenuous exercise, drugs (EtOH, aspirin, narcotics)

myoglobin

heme protein that is rapidly released from damaged tissue in the bloodstream

myoglobin is found in high concentrations within

skeletal muscle and heart tissue

smaller molecule detected in the serum earlier than CK-MB or troponins but LESS specific for myocardial necrosis

myoglobin

myoglobin is the

first to appear, first to peak, first to decline

myoglobin may be detected . . .

as early as 2 hrs after the onset of myocardial necrosis→ HOWEVER not cardiac specific

myoglobin peaks

within 4-12 hrs and then immediately returns to baseline levels

myoglobin is excreted in the

urine and can be elevated d/t poor renal clearance

myoglobin has ________ sensitivity

HIGH

negative myoglobin within the first several hours after the onset of chest pain can be useful in r/o an acute MI

myoglobinuria is not used in

the diagnosis of ACS

if myoglobinuria is positive it suggests

non-cardiac source

myoglobinuria can be ________ after fevers, infections, trauma

falsely elevated

myoglobinuria→ urine test

urine test that is measured at rest and after exertion

• indicated to r/o rhabdomyolysis, metabolic disorders, mitochondrial disorders